Studies of bacterial iron metabolism are underway in the following areas: (1) Iron transport. The role of the natural ferric chelating secondary hydroxamates as iron transport cofactors is being defined. Interest centers on isolation of the membrane-bound and soluble components of the ferric hydroxamate transport system to delineate the various steps of the process, to study its mechanism of energization, and to determine the method of iron release from the chelates. (2) Role of iron in cell division and metabolic regulation. Evidence has been adduced that some ferric hydroxamates are cell division activators in bacteria. Selective starvation for iron, but not other metals, causes preferential inhibition of DNA replication in both bacterial and mammalian cells. Protein and RNA synthesis appear unaffected. Because of the link between chromosome replication and cell division, experiments have been designed to determine if iron-starvation halts initiation of DNA replication or stops continued DNA synthesis (in both procaryotic and eucaryotic cells) to gain an understanding of the participation of iron in control of cell division. Iron-deprivation also alters certain transfer RNA species and may cause changes in some aminoacyl-tRNA synthetases in bacteria. Isolation of the altered aminoacyl-tRNA synthetases and studies of their properties and possible role in regulation of protein synthesis are underway.